David Cameron will bring his EU message to Scotland next week, defying SNP calls for him to stay away, and making his first visit north of the border since Downing Street signalled this week that Brexit could lead to a second independence referendum.

No 10 confirmed the visit – expected to coincide with the Scottish Conservatives’ spring conference in Edinburgh – as George Osborne emphasised that, should Britain vote to leave the EU, it would cause a “profound economic shock”.

The Prime Minister will repeat his “better together” mantra during a campaign trip to Cardiff today, firing off several statistics to underline his argument that the UK is “better off” in the EU. These include how nearly half of Welsh trade is with the EU and some 100,000 Welsh jobs are linked to exports to EU countries.

Mr Cameron is expected to repeat the exercise, using pro-EU Scottish statistics provided by the Treasury, when he visits Scotland next week. Tomorrow, he will hit the EU stump in Northern Ireland; Northern Ireland Secretary Theresa Villiers is pro-Brexit.

Speaking in Shanghai, where he is attending a meeting of G20 finance ministers, the Chancellor warned the UK faced more risks of economic uncertainty than at any time since the financial crisis of 2008.

In what some will regard as a swipe at the Outers, Mr Osborne said talk of Brexit was "not some political parlour game", highlighting the recent fall in the value of the pound.

"This is about people's jobs and their livelihoods and their living standards,” declared the Chancellor.

“In my judgement as chancellor, leaving the EU would represent a profound economic shock for our country, for all of us and I'm going to do everything I can to prevent that happening," he said.

Mr Osborne’s intervention came amid suggestions he is pushing the G20 group of leading economies to warn about the dangers of Britain leaving the EU. No 10 noted how the subject was not part of the formal agenda but it was “normal” for the G20 to discuss global risks.

No 10 confirmed that Whitehall would produce a series of documents – similar to the exercise during the Scottish independence referendum campaign – to set out the Government’s assessment of the issues in a “factual and balanced way”. These would include looking at the alternatives to EU membership, the process of leaving and the costs and benefits of membership. Anti-EU MPs have called for there to be an “independent” costs and benefits assessment.

Downing Street indicated that pro-Brexit ministers would not be given access to the documents ahead of publication under the terms of an arrangement where Whitehall papers on the referendum are not being made available to ministers campaigning against the UK Government position in a personal capacity.

Earlier, Mr Cameron suffered a blow when his mentor and predecessor as Tory leader, Lord Howard, came out against Britain’s membership of what the peer called a “outdate, flawed and failing” EU. He insisted Britain should have the “self-belief” to go its own way.

Suggesting that a vote for Brexit would force Europe's leaders back to the negotiating table, the Conservative peer told BBC Radio 4’s Today programme: "If they were really faced with a British vote to leave, they would think again.

"But I could be wrong. And if I'm wrong, it would just mean that they have finally refused to face up to the need for the fundamental and far-reaching reform that David Cameron set out to achieve. And if they are not prepared to reform, we are better out," he argued.

Mr Cameron has vowed to trigger Article 50 of the Lisbon Treaty, beginning the process to leave the EU, as soon as possible after the referendum, if the UK votes to sever ties with Brussels.

But Lord Howard suggested a pause of up to a month might be advisable to enable EU leaders to come back with a better deal for Britain.

"Is quite likely that during that month they would say: ‘Let's talk some more, let's see if we can reach a different agreement,’ and perhaps you could have a second referendum. If, after a month or so they don't, then Article 50 would have to be triggered and negotiations to leave would begin," he said.

But in response, the PM’s spokeswoman said, that while Mr Cameron had “great respect” for his mentor and predecessor as Tory leader, there was only one choice on the ballot paper; remain or leave.

Stressing how EU partners had been clear, that the deal agreed last week would be off the table if Britain backed Brexit, she noted that, in such circumstances, a No vote would be a “leap into the dark”.

Rebuffing Lord Howard’s suggestion of a post-Brexit renegotiation before a possible second poll, the spokeswoman added: “The idea that the British people could decide to leave and then the Government would not just act on that is for the birds; it’s not just something that is going to happen.”

In a separate development, reports suggested that two UK cabinet ministers, the pro-EU Anna Soubry and the anti-EU Chris Grayling have agreed to debate EU membership at an event in Westminster, chaired by BBC broadcaster Jeremy Vine.

Meantime, Mr Osborne has been criticised by Tory Eurosceptics for breaking convention by commenting on the future direction of the exchange rate of the pound when warning against Britain leaving the EU.

Conservative backbencher Philip Hollobone derided the Chancellor's "spin" as he accused the UK Government of being afraid of commissioning an independent assessment of the costs and benefits of EU membership.

The Kettering MP said that, in any case, a decrease in the value of the pound would be "extremely good news" for British exporters.

He spoke as MPs debated prominent Leave campaigner Peter Bone's EU Membership (Audit of Costs and Benefits) Bill, which would appoint an independent commission to analyse the pros and cons of remaining in the union.

Elsewhere, Willie Walsh, the boss of the firm which owns British Airways, said Brexit would not have a "material impact" on the airline’s business.